The present invention is generally related to semiconductor lithography techniques and equipment, and more particularly to extreme ultraviolet (EUV) lithography.
The recent trend towards the miniaturization of electronic circuits is driven by consumer demand for smaller and light-weight electronic devices such as cellular phones, PDA""s and portable computers, for example. Optical projection lithography is a lithographic technique where light is refracted through camera lenses onto a masked semiconductor wafer to pattern a particular layer. This lithographic technique is currently used for the high volume manufacture of circuits having etched circuit lines of 0.18 micron dimensions or greater in width. However, the present technology for optical projection lithography cannot produce circuits with substantially smaller features due to fundamental physical limitations on the ability to focus lightxe2x80x94smaller circuit features require a source of shorter wavelength light.
An emerging next-generation lithographic (NGL) technique in semiconductor technology is extreme ultraviolet (EUV) lithography, an advanced technology for making integrated circuits smaller and more powerful. In EUV lithography, intense beams of very short wavelength ultraviolet (UV) light are reflected from a circuit design pattern and refracted by mirrors through camera lenses into a silicon wafer.
A candidate technology for a practical EUV light source is a laser-produced plasma (LPP). In a LPP EUV source, a target material is illuminated by a high-power laser to produce a very high temperature plasma which radiates the desired EUV light. The present invention pertains to a light source in which a condensable gas (vapor) is passed through a nozzle assembly in such a manner so as to produce a jet or spray containing a plurality of small droplets along with some uncondensed gas. This plurality of droplets serves collectively as the target of the laser.
The present invention achieves technical advantages as a gas jet nozzle having a housing with a secondary channel for gas flow that restricts the lateral expansion of gas flowing from the primary channel. In one embodiment, a gas jet nozzle for an extreme ultraviolet (EUV) light source comprises a housing having a primary channel adapted to couple to a primary gas source and expel a first gas/droplet stream. The housing also includes a secondary channel proximate the primary channel adapted to couple to a secondary gas source and adapted to expel a second gas stream. The second gas stream shapes the first gas/droplet stream expelled by the primary channel.
Also disclosed is a gas jet nozzle system for an extreme ultraviolet light (EUV) source, comprising a primary gas source, a secondary gas source, and a housing. The housing comprises a primary channel coupled to the primary gas source and adapted to expel a first gas/droplet stream. The housing further comprises a secondary channel proximate the primary channel coupled to the secondary gas stream. The housing secondary channel is adapted to expel a second gas stream to shape the first gas/droplet stream expelled by the housing primary channel.
Further disclosed is a method of converting laser energy to EUV energy, comprising the steps of expelling gas from a nozzle and illuminating the expelled gas with a laser to produce EUV light-emitting plasma. The nozzle comprises a housing having a primary channel and a secondary channel proximate the primary channel. The primary channel is coupled to a primary gas source, and the secondary channel is coupled to a secondary gas source. A first gas/droplet stream is expelled from the primary channel and a second gas stream is expelled from the secondary channel, where the second gas stream shapes the first gas/droplet stream.
Advantages of the invention include the ability to illuminate the stream expelled from the primary channel with a laser at a distance further away from nozzles of the prior art without the loss of performance that would occur due to spreading of the expelled stream in the prior art. This is beneficial because damage to the nozzle from the generated high temperature plasma is significantly reduced, resulting in longer life of the nozzle and saving replacement costs. Furthermore, costs are reduced for replacing collection optics that become contaminated by the nozzle erosion by-products. The life of the collection optics is further increased by the fact that the secondary shroud gas flow serves to directly block some of the very fast atoms or ions emitted from the plasma that would otherwise impinge upon and erode the collection optics. Also, the nozzle of the present invention blocks a smaller fraction of the emitted EUV light from reaching the collection optics, as compared to the prior art.